Aircraft guidance, approach, and landing system with yaw detection and metering



AMPLIFIER INVENTOR ATTORNEYS N m T C E R D l L F l0 E,L GUIDE CURRENTWIRE ON AHjCRAFT AMP. 75

R. GUNN LANDING STRIP Sept. 20, 1966 AIRCRAFT GUIDANCE, APPROACH, ANDLANDING SYSTEM WITH YAW DETECTION AND METERING Original Filed April 29,1959 AMPLIFIER 34 SYN CHRONOUS RECTI FER 93 l. A J

SOURCE OF A.C. EXCITING POWER APPROXIMATE LINE OF FLIGHT United StatesPatent 3,274,546 AIRCRAFT GUIDANCE, APPROACH, AND LAND- ING SYSTEM WITHYAW DETECTION AND METERING Ross Gunn, 4437 Lowell St. NW., Washington,D.C. Original application Apr. 29, 1959, Ser. No. 809,861, now PatentNo. 3,116,473, dated Dec. 31, 1963. Divided and this application Oct.30, 1963, Ser. No. 320,113 6 Claims. (Cl. 34025) This application is adivision of application Serial No. 809,861, filed April 29, 1959, nowPatent No. 3,116,473.

This invention relates to guidance, approach, and landing systems,primarily intended for, but not restricted to use with aircraft, andmore particularly to such systems making use of closed loop,alternating-current-excited conduction systems for height anddirectional guidance in cooperation with aircraft carried positiondetection and indication systems and incorporating yaw detection andmetering.

It is a general object of the present invention to provide novel andimproved aircraft guidance systems of great simplicity and reliability,low cost, high degree of accuracy, and capable of operation with aminimum of attention by the pilot.

More particularly, it is an object of one phase of the present inventionto provide a closed A.C.-energized guidance system for two-way aircraftoperation, making use of signals from one side of the loop for guidancein one direction and from the other well-spaced-away side for guidancein the other, means independent of the degree of visibility beingprovided for ready ascertainment of correct direction of flight overeither loop side.

In another phase of the system, it is an object to provide aircraftcarried instruments, cooperating with the signals from an energizedguide loop system on the ground or with the signals from an energized,concentrated con ductor using a dispersed return conduction system, fordetecting and metering yaw for both direction and degree whereby propercorrective measures may be taken, just prior to landing to correct theyaw for aircraft set-down aligned with the axis of the landing strip.

For use with both phases of the system referred to above, it is anobject to provide an additional, optional means for transmitting asynchronizing signal, making use of electrostatic induction from aconductor paralleling the main signal or guide conductor, energized at ahigh voltage usually in respect to ground at the same frequency andhaving a fixed phase relation to the current in the guide conductor andpicked up on the aircraft by an antenna, amplified and used forsynchronizing an instrument actuating rectifier system thereon in amanner not capable of radio jamming.

An important object of the invention resides in the arrangement on theaircraft of two signal detecting coils, one mounted with its axistransverse to the flight axis and thus responsive to the component ofthe guide conductor field which is horizontal and perpendicular to thenormal flight axis of the aircraft, and the second being arranged torespond to the component of the guide conductor field which is parallelto the fore and aft axis of the craft, with means associating theoutputs of the two coils to sense yawing in direction and degree.

Still another object of the invention resides in an arrangement wherebythe yaw measuring means is dependent only on the angle of yaw and not onthe intensity of the magnetic field inducing the voltage in the yawresponsive coil, whereby the effectiveness of the system is independentof the distance (within limits) of the aircraft from the guideconductor.

Other and further objects and specific features of the invention will bemore apparent to those skilled in the ICC art upon a consideration ofthe following specification and accompanying drawing wherein aredisclosed several exemplary embodiments of the invention with theunderstanding that such changes and modifications may be made therein asfall within the scope of the appended claims without departing from thespirit of the invention.

In said drawings:

FIGURE 1 is a diagrammatic and schematic showing of the groundinstallation of a closed loop guidance, approach, and landing systemillustrating one method of synchronizing craft carried instrumentationfor advising the course, location, elevation, etc.;

FIGURE 2 illustrates craftborne apparatus for normal guidance andlanding operations;

FIGURE 3 is a schematic showing of one method of mounting the guideconductor and an auxiliary conductor for synchronization by means ofelectrostatic induction;

FIGURE 4 is a diagrammatic showing of craftborne equipment for use withthe electrostatic synchronization system of FIGURE 3; and

FIGURE 5 is a diagrammatic showing of the circuits aboard the craft fordetermining and indicating or metering yaw.

In that system are disclosed two induction coils mounted on the craft towork in conjunction with signals from the energized conductor andsynchronizing signals to provide accurate data to guide an airplane to aperfect landing. The two mutually perpendicular magnetic induction coilshave, respectively, such orientation as to present one axis horizontaland transverse to the line of flight, and one vertical or normal to theground, thus responding respectively to a component of the excitedconductor field which is horizontal .and perpendicular to the normalaxis of flight of the craft, and to one which is vertical andperpendicular to the axis of symmetry (fore and aft axis of theairplane).

These coils work satisfactorily where the aircraft axis and the flightdirection are identical and in conjunction with appropriate metersenable the pilot to follow directly above the guidance conductor todetermine his height above the conductor whereby safe landings may bemade under condition of poor or non-existent visibility; however, if dueto strong cross winds the plane is caused to yaw, the response of one ofthese coils may change appreciably; and moreover, it is desirable toknow the direction and degree of yaw in order to eliminate it by properuse of the rudder just before touchdown, for otherwise the craft willinstantly run off the landing strip laterally.

For the purpose of detecting the presence of yaw and determining itsextent and direction, a third coil whose axis is perpendicular to eachof the two mentioned above may be provided. Its response axis is foreand .aft and hence at right angles to all electromagnetic fields fromthe guide conductor if the aircraft has its flight axis substantiallyparallel to the conductor. When yaw occurs, however, this coil willsense a magnetic field because the flight axis presumably parallel tothe conductor, and the aircraft axis make an angle to each other. Themagnitude of the voltage induced in this third coil depends not only onits distance from the guide conductor and the current in the conductor,but on the sine of the angle of yaw. Moreover, it may be demonstratedexperimentally that the phase of the induced voltage in the coilreverses whenever the angle of yaw reverses.

Referring now to the drawings and first to FIGURE 1 there is shown anarrangement of guide conductor 10 in the form of a loop which may extendfrom city 11 to city 12 with the sides 14 and 15 thereof spaced on theorder of a thousand feet apart, whereby separate guide paths areprovided for incoming :and outgoing trafiic at each landing strip 11 and12, crafts travelling in opposite directions being maintained at a safelateral spacing by the rotary trafiic.

It is contemplated the closed loop may be used with cities as far apartas 100 miles, but in cases where the distance is greater or theintermediate terrain undesirable for positioning the guide conductors, aclosed loop may be provided at each end adjacent the landing strip, inwhich event, intermediate portions of the side conductors 14 and 15 maybe eliminated. This provides for adequate guidance for approaching bothlanding strips and insures the proper rotary operation of traffic.

The conductor loop is energized with an A.C. current of constant andknown magnitude for signalling aircraft through a transformer energizedby a suitable source of A.C. power having a frequency usually within theaudio range. If the loop is divided into two parts by shortingconductors as note-d above, a separate transformer for exciting theupper section, a substantial duplicate of that shown at 20, will berequired.

For providing a synchronizing signal for use aboard the aircraft, aradio transmitter such as indicated at 22 may be located anywhere alongthe loop length and has its signal modulated by transformer 23 whoseprimary is excited, for example, by a transformer in series with theguide conductor loop and, hence, provides the same frequency modulationas the magnetic field energy given off electromagnetically by thealternating current. Other methods of coupling to the modulator of theradio transmitter are acceptable. In the event that the distance betweenlanding strip-s is too great for reliability to be placed on a singletransmitter at one end of the loop, a second one may be providedadjacent the opposite end and similarly excited.

-For guidance, elevation information, and landing, as described in thepreviously-identified pending application, each aircraft may be equippedwith apparatus as indicated in FIGURE 2 where two independentperpendicularly arranged sensing or pick-up coils of many turns of smallwire are oriented to lie, one, numbered 30, in a horizontal plane withits axis vertical so as to be responsive to the vertical component ofthe varying magnetic field established by the current in the guideconductor, while the second, numbered 31, is responsive to thehorizontal component of the field and has its axis horizontal andperpendicular to the fore and aft axis of the craft.

Under adverse conditions these coils should be maintained substantiallyin their original horizontal and vertical orientation by the use ofgimbals, gyroscopic controls, or other means so that even though thevehicle tips to relatively large angles, they will remain essentially intheir respective horizontal and fore and aft vertical planes for propercooperation with magnetic signals from the guide conductor. Therelatively small A.C. voltage induced in the coils may be amplified asby known type amplifiers 33 and 34, respectively, and their outputs are,via transformers 35 and 36, connected respectively to a center zerodirect current meter 38 and a conventionally scaled direct current meter39, each shunted by an appropriate condenser 40 and sensitivity adjuster41. The outputs from the two amplifiers are rectified before beingsupplied to the meters 38 and 39 by a single rectifier 37 including avibrating reed 42 connected to the common conductor 44 between thesecondaries of transformers 35 and 36, via the meters and their shuntingcondensers 40 and is oscillatable between stationary contacts 45 and 46connected respectively to the other side of each meter and condenser viathe transformer secondaries.

The reed 42, which acts in conjunction with contacts 45 and 46 arerectifying the outputs of amplifiers 33 and 34 in order that directcurrent meters may be used, is vi brated by polarized relay mechanismincluding a coil 48 energized from phase adjuster 50 and permanentmagnet 49 which may or may not be secured to the reed.

Operating energy for the coil 48 comes from radio receiver 63 energizedby antenna 61 and counterpoise 62 carried by the craft. This delivers todetector 64 and amplifier 65, energizing the phase adjuster throughtransformer 66. Energy in coil 48 vibrates reed 42 causing synchronousand individual rectification of the outputs of amplifiers 33 and 34. Thephase adjuster must be carefully manipulated, in the original setting ofthe apparatus, to insure synchronism, for the radio signal provides areference frequency on the aircraft which is exactly the same as thatused to excite the guide conductor and must bear a fixed phase relationto it so that the rectifier contacts may be caused to open and close insynchronism with the exciting current in the cable and thus therelatively weak voltages induced in coils 30 and 31 may be rectified andtheir magnitudes and the phase of the current in coil 30 read on themeters 38 and 39 thus making it a simple matter to find the guideconductor and to detect its influence at relatively high altitudes underconstant conditions of excitation.

As pointed out in the earlier application, the polarized relay as arectifier is subject to certain ills, and circuits without movingcontacts are frequently desired. For this purpose the well-knownsynchronous detector amplifier may be used to accomplish the sameresults and the outputs from such circuits will operate direct currentmeters, giving readings that are proportional to the alternatingvoltages applied and will reverse the readings of the direct currentmeter connected to coil 30 when phase reversal occurs. This arrangementis shown in FIGURE 4 of the co pen-ding application previouslyidentified.

Other specialized circuits for accomplishing the same objective may befound in electronic literature.

In the prior application two methods of providing a synchronizing signalfor actuating the rectifiers were disclosedthe first being an amplifiedsignal from coil 31 responsive to the guide conductor pulses, for, aslong as the craft is travelling in the same direction, this signal doesnot change phase. However, it is commonly of less intensity than theradio signal defined above and forming the second method forsynchronization. Obviously the radio method is superior because itpermits operation at greater distances from the conductor, simplifyingthe problem of locating it in overcast weather. Moreover, the radiosignal does not change phase when the direction of the craft in respectto the guide wire is reversed, but the signal received by coil 31 doeschange phase under the same circumstances; and if this signal is usedalso for operating a synchronous rectifier, it is not possible to tellin which direction the craft is moving in respect to the guideconductor. With radio, however, this can be done simply by deviating thecraft from the plane of the conductor and noting whether the meter 38indicates deviation in the direction in which the craft is deviating oroppositely. Signals from the coil 31, as pointed out in the earlierapplication, are varied in intensity almost exactly in inverseproportion to the height of the craft above the guide conductor, andthis height can be read on a carefully graduated instrument such as 39,which can also be useful in enabling a determination of the direction ofthe craft along the guide wire.

A third method, to be used in addition to the magnetic and radio systemsalready described for maintaining synchronism for the rectifiers, isillustrated in FIGURES 3 and 4, and this system employs electrostaticinduction.

The third method involves the use of a second unshielded wireparalleling and somewhat remote from the guide current wire in, forinstance, an arrangement such as shown in FIGURE 3 where a pole 75carries the guide current wire 10 at one end of a crossarm and at areasonable distance above the ground, and a second wire 76 is supportedat the top of the pole more or less parallel to the guide conductor; andthis second wire is maintained at a high alternating current voltageusually with respect to ground by transformer 79 powered from source 80,as in FIGURE 3, at the same frequency as the current in 10. Itsfrequency is identical with that current,

3 and the phase has a fixed relationship to the current in the guideconductor.

If an aircraft is within fifteen hundred to twenty-five hundred feet ofthis high voltage wire or nearer, a small antenna such as illustrated at77 in FIGURE 4, on the aircraft, will have a small voltage induced in itwhose frequency is exactly the same as that of the high voltage, which,in turn is identical with the frequency of the current in the guideconductor. If this small signal is passed through amplifier 78, analternating current voltage may be secured on the aircraft that has allof the required characteristics to operate the synchronous rectifier, alocked-in amplifier, or a synchronous detect-or if introduced intotransformer 66 of FIGURE 2.

For certain reasons the electrostatic induct-ion method of providing asynchronizing signal on the aircraft is not as useful as the radiomethod and may be more expensive, for it cannot operate with a buriedconductor because the conducting earth would shield the electrostaticfield from the aircraft. Electrostatic synchronization could be veryuseful if a landing area were subject to radio jamming of accidental orintentional origin and radio circuits could not be used.

The apparatus defined above comprising the oriented magnetic inductioncoils mounted on the aircraft and working in conjunction with an excitedguidance conductor on the ground provides accurate data to guide theairplane to a perfect landing. For the purpose of the above-describedfeatures of the invention, the induction coils on the aircraft weredefined as air core inductors Wound on a frame defining a planeperpendicular to the axis of maximum response to the magnetic field, butfor those phases of the invention and the one about to be described, ithas been found that such coils could be of wire wound on a thin magneticalloy core, like annealed Permalloy or Allegheny Ludlum 4750 alloy. Thedirection of maximum response is in this case the direction oforientation of the straight core axis. Either type of coil is wound withmany turns of wire and is designed to be responsive to small alternatingmagnetic fields as previously explained.

For yaw measuring, two pick-up coils are desirable, and one is mountedon the aircraft in such a way as to respond to the components of theexcited conductor field which are horizontal and perpendicular to thenormal flight axis of the airplane. As seen in FIGURE 5, this coil isnumbered 31 since it may be one of the coils bearing that number used inthe apparatus of FIGURE 2, in order to prevent duplication. The othercoil 82 is arranged with its axis of response parallel to the fore andaft axis of the airplane and is preferably also stabilized by gimbals ora small gyroscope so that it responds to the components of the impressedmagnetic field which are parallel to the axis of symmetry of the craftin spite of the attitude thereof. Thus since the magnetic field of theguide conductor is always at right angles to the conducting axis, therewill be no electromotive forces induced in coil 82 if the direction ofmaximum magnetic field response of the coil is parallel to the fore andaft axis of the airplane when the aircraft axis and the flight axis areidentical or parallel, and in the plane of the conductor.

However, if the airplane yaws due to a cross wind, for example, coil 82will sense a magnetic field because the flight axis and the aircraftaxis make an angle with each other. An examination of the basic physicsshows that the magnitude of the voltage induced in the coil dependsinversely on the distance of the coil from the guide conductor, thecurrent in the latter, and on the sine of the angle of yaw. Clearly thephase of the induced voltage reverses whenever the angle of yawreverses.

As shown in FIGURE 5, coil 31 is connected through a potentiometer 83 toamplifier 84, the out-put of which is fed through a transformer to anytype of rectifier 85, the output of which is regulated by potentiometer86, it

6 being noted that the rectifier is poled to provide a negativepotential on conductor 87 and positive on conduc tor 88.

Coil 82 has its output fed to the grid and filament of the first tube ofan amplifier 90, as shown, by way of potentiometer 94 and condenser 96,and the output of the amplifier passing through transformer 91 is fed toa center-zero direct-current meter by way of a synchronous rectifier 93,rectification being achieved and synchronized as previously defined bymeans of a signal having the same frequency and phase as that of theguide conductor.

Since coil 82 is responsive to the longitudinal components of themagnetic field with respect to the axis of symmetry of the plane andwill reverse its sine as the angle of yaw is reversed, it is operated inconjunction with the synchronous rectifier and will serve as the mostuseful yaw indicator. If it is desired to modify the yaw indicator toprovide an angular measure of yaw, certain refinements are required tocompensate for the difference in the magnitude of the signal induced inthe sensing coil resulting from different altitudes of the landingaircraft and, hence, different intensities of field.

In general, a yaw meter is required on an aircraft only when the lattercontemplates contact with the ground, i.e., during the later stages ofthe approach, and the signal introduced into the yaw coil by the AC.magnetic field of the cable will normally vary by a factor ofapproximately 5 when the aircraft drops from 200 feet, say, down toground contact. Only over this limited range is it required to make theyaw meter readings dependent only on the angle of yaw and not on theintensity of the magnetic field inducing a voltage in the coil. This isWhere the secondary sensing coil 31 and its amplifying system, alreadydescribed above, comes into operation to provide a signal which,interacting with the sig nal from the yaw-sensing coil, is arranged tocompensate for the increased signal resulting from decreasing altitudesof the aircraft. In other words, the coil which is responsive to thehorizontal transverse component of the magnetic field is used, toprovide a voltage that increases with decreasing altitude, in such a wayas to compensate for the increase in signal from the yaw-sensinginduction coil. The circuits shown are more or less equivalent to anautomatic volume control system, employing vacuum tubes or transistorsto perform the requisite control. As shown, the output from rectifier 85is fed to the filament and grid of the first tube in amplifier 90, thenegative lead 87 through voltage divider 94 along which a slider 95connected to coil 82 moves. Thus, the output from rectifier 85 changesthe effective amplification of the tube as the altitude of the aircraftvaries. The closer the craft to the guide conductor, the more effectivethe signal suppression becomes so that the amplification factor of thetube is reduced, when the yaw signal increases solely due to a loweringin altitude.

The secret of the operation of this system just described is that thedirect current voltage received from coil 31 will change very littlesolely for appreciable changes in yaw, and thus can be introduced intothe yaw-indication circuit as discussed previously to decrease themagnitude of the yaw-induced voltages in such a way that the yaw anglecan be determined with useful accuracy. The reason for the relativeinsensitivity of coil 31 is that its output changes with the cosine ofthe angle of yaw as distinguished from that of coil 82 which changeswith the sine of the angle of yaw.

Clearly the auxiliary voltage derived from the coil responsive to thetransverse field need not be applied to the tube grid exactly as pointedout, but may be used in other known ways by connection to the screen orplate circuits or otherwise so that the auxiliary voltage acts topartially block the amplification of the signal from the yaw-sensitiveinduction coil. The adjusting devices shown in the several circuitspermit regulation so that the reading of the DC. yaw meter does notchange appreir v y' 7 ciably with distances (within the limits stated)vertically above the guide conductor. It is thus responsive principallyto the angular yaw of the aircraft with respect to the projected planedefined by the position of the guide conductor, so that it leads to themeasurement of the angle of yaw and not of the height of the aircraftabove the excited guide conductor. The device can then be calibrated interms of degrees.

Since the several inventions defined herein are of primary usefulness inconnection with the flight of aircraft, the inventions have been sodescribed, but it will be readily appreciated that they are of equaladvantage, for instance, for the guidance of ships in harbors, bays, orrivers where fog makes visibility insufiicient for visual navigation.With slight modifications such as the elimination of the coil 31, thedevice may also be useful in connection with the guidance of roadvehicles. Since these would never vary substantially in height above theguide conductor, no adjustment would be necessary to insure properoperation of the yaw feature.

Ideally, one would like to have the guide conductor extend outwardtoward the approaching airplane in a straight line and at the same levelas the touchdown point. Actual terrain seldom permits this, and theguide conductor lies above or below the ideal position. Clearly if theactual guide conductor is appreciably below the ideal level, morecurrent should flow in this section of the conductor to bring thedesired magnetic field to values characteristic of the ideal magneticlanding pattern. Conversely, if the conductor is above the idealposition, less current is required. Engineering this non-uniformdistribution designed to compensate for irregularities of terrain iseasily accomplished by the use of auxiliary transformers and/orconductors excited from the same (power source or at least one of thesame frequency and appropriate phase as used to excite the main guideconductor.

I claim:

1. A guidance system for vehicles including, in com bination, means forgenerating a pattern of alternating magnetic flux at least within theaudio range, induction means on a vehicle for sensing said flux as anA.C. voltage, means on the vehicle to rectify said voltage, means toindicate the phase direction of the flux from said rectified voltage, aconductor positioned above ground and within the influence of saidpattern of AG. magnetic flux, means energizing said conductor with ahigh AC. voltage of the same frequency as said pattern, and means on thevehicle to detect the electrostatic flux from said conductor, said meansto rectify said voltage sensed from the pattern flux being synchronizedby the detected electrostatic fiux to insure correct indication ofphase.

2. The guidance system of claim 1 in which the generated pattern is alinearly extended one for aircraft landing guidance.

3. In a guidance system for vehicles, in combination, a guide conductorover which vehicles travel and a return circuit spaced sufficiently farapart to eliminate interference, means energizing said conductor withalternating current of such frequency as to cause only inconsequentialphase displacement of the current throughout the conductor length,induction means on said vehicle for sensing the changing guide conductorflux, means for indicating the phase direction of the changing guideconductor flux, an unshielded second conductor adjacent said guideconductor and above ground level, means energizing said second conductorwith a high A.C. voltage of the same frequency as that in the guideconductor, means on each vehicle to detect the electrostatic flux fromsaid second conductor, rectifying means to rectify the voltage output ofsaid induction means, and means energized by said detected electrostaticflux to synchronize the operation of said rectifying means with thecurrent in the guide conductor.

4. The guidance system of claim 3 including means to indicate the phasedirection of the flux from said rectified voltage.

5. In a system for providing guidance signals to a flying aircraft, incombination, means substantially at ground level for establishing apredetermined and uniform average level pattern of changing magneticflux distributed along an extended guide path, means energizing saidmeans with an alternating current of such frequency approximately withinthe audio range as to cause only inconsequential phase displacement ofthe current throughout the said path, means to establish an associatedand similarly distributed pattern of synchronously changingelectrostatic field from the said alternating current energizing means,inductor means on an aircraft for sensing the changing magnetic flux,antenna means on the aircraft for receiving the changing electrostaticfield, a direct current device for indicating the phase direction of thecurrent received by said inductor means, rectifying means for saidcurrent from said inductor and means actuated by the antenna output forsynchronizing the rectifier output with the magnetic flux from saidpattern.

6. Means for developing phase indicative signals on aircraft from anestablished ground level source of changing magnetic flux distributedalong a guide path, comprising providing an above ground sourcecontiguous to said first source of an electrostatic field synchronouslychanging in phase with the first source, a rectifier on said aircraft, asignal pickup on said aircraft for said magnetic flux, a signal pickupon the aircraft responsive to said electrostatic field, means supplyingthe rectifier with the output of said first pickup for rectificationthereof, means supplying said rectifier with the output of said secondpickup for synchronization of the rectifier output with the saidchanging magnetic flux, and a direct current meter energized by saidrectifier output and indicative of the direction of direct current flowthereto.

References Cited by the Examiner UNITED STATES PATENTS 1,968,068 7/1934Blancard et al. 343-1012 2,339,291 1/1944 Paulus et al 340-4 X 2,428,36010/1947 Dingley 340-4 NEIL C. READ, Primary Examiner.

A. H. WARING, Assistant Examiner.

1. A GUIDANCE SYSTEM FOR VEHICLES INCLUDING, IN COMBINATION, MEANS FORGENERATING A PATTERN OF ALTERNATING MAGNETIC FLUX AT LEAST WITHIN THEAUDIO RANGE, INDUCTION MEANS ON A VEHICLE FOR SENSING SAID FLUX AS ANA.C. VOLTAGE, MEANS ON THE VEHICLE TO RECTIFY SAID VOLTAGE, MEANS TOINDICATE THE PHASE DIRECTION OF THE FLUX FROM SAID RECTIFIED VOLTAGE, ACONDUCTOR POSITIONED ABOVE GROUND AND WITHIN THE INFLUENCE OF SAIDPATTERN OF A.C. MAGNETIC FLUX, MEANS ENERGIZING SAID CONDUCTOR WITH AHIGH A.C. VOLTAGE OF THE SAME FREQUENCY AS SAID PATTERN, AND MEANS ONTHE VEHICLE TO DETECT THE ELECTROSTATIC FLUX FROM SAID CONDUCTOR, SAIDMEANS TO RECTIFY SAID VOLTAGE SENSED FROM THE PATTERN FLUX BEINGSYNCHRONIZED BY THE DETECTED ELECTROSTATIC FLUX TO INSURE CORRECTINDICATION OF PHASE.